Fig. 5. The addition of 10 mM HU to developing gametophytes of M. vestita at various times after imbibition shows that the cells remain permeable to small molecules for 
3 hours. (a) HU was added 60 minutes after imbibition and fixed 8 hours after imbibition; arrest occurred after the second cell division cycle. (b) HU was added 120 minutes after imbibition and fixed 8 hours after imbibition; arrest occurred after the second cell division cycle. (c) HU was added 180 minutes after imbibition and fixed 8 hours after imbibition; arrest occurred during the fourth cell division cycle. (d) HU was added 200 minutes after imbibition and fixed 8 hours after imbibition; there was no mitotic arrest, and spermatids developed normally. (e) Anti-centrin antibody immunolocalization of a gametophyte treated with HU, 120 minutes after imbibition. The antigen distribution is heavily concentrated in the spermatogenous cells at the time of fixation, 8 hours after imbibition. This pattern of distribution does not at all resemble the localization pattern observed in normal spermatids (Klink and Wolniak, 2001) (f) Anti-ß-tubulin antibody localization of a gametophyte treated with HU, 120 minutes after imbibition. The antigen abundance in spermatogenous cells is normal at the time of fixation, 8 hours after imbibition, although the distribution within these cells is anomalous (Klink and Wolniak, 2001). All gametophytes were photographed with DIC. Bar, 25 µm.
